归并排序：

int tmp[N];
void merge_sort(int q[],int l,int r)
    {
        if(l==r) return;
        mid=r+l>>1;
        merge_sort(q,l,mid);
        merge_sort(q,mid+1,r);
        int i=l,j=mid+1,k=0;
        while(i<=mid&&j<=r)
        {
            if(q[i]<=q[j]) tmp[k++]=q[i++];
            else tmp[k++]=q[j++];

        }
        while(i<=mid) tmp[k++]=q[i++];
        while(j<=r) tmp[k++]=q[j++];
        for(int i=l,j=0;i<r,j<k;i++,j++) q[i]=tmp[j];
    }